<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta http-equiv="X-UA-Compatible" content="IE=edge">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Document</title>
</head>
<style>
.box{
	height: 500px;
	width: 1000px;
	background-color: aliceblue;
	margin: 0 auto;
}
.center{
	height: 100px;
	width: 100%;
	background-color: red;
	float: left;
}
.content{	
	height: 100px;
	background-color: aqua;
	/* 核心代码：留白 */
	margin-right: 50px;
	margin-left: 100px;
	
}
.left{
	height: 100px;
	width: 100px;
	background-color: green;
	float: left;
	/* 核心代码 */
	margin-left: -100%;
}
.right{
	height: 100px;
	width: 50px;
	background-color: yellow;
	float: left;
	/* 核心代码 */
	margin-left: -50px;
}
</style>
<body>
	<div class="box">
		<div class="center">
			<div class="content">内容</div>
		</div>
		<div class="left"></div>
		<div class="right"></div>
	</div>
</body>
</html>